There exists a great need for copper alloy for electrical purposes where, aside from high solidity and high electrical conductivity, resistance against softening and oxidation is needed. These alloys are needed as base materials for semiconductors, for example for transistors or integrated circuits. Base materials for semiconductors must have certain characteristics:
(a) The mechanical solidity must be sufficiently high so that an inherent stability of the base is assured during manufacture, during transport, and when equipping it with electronic structural elements. The hardness should therefore lie, if possible, above 125 HV (Vickers hardness). On the other hand, the flexibility of the material must be sufficient so that the small connecting legs do not break off during repeated back and forth bending. Usually, a three-time bending corresponding with German industrial standard (DIN) 50153 is here requested. PA1 (b) The material must resist softening, so that the steps which are needed during the semiconductor manufacture and which are carried out at a high temperature do not result in a loss of the hardness and inherent stability. A measure for the softening resistance is the so-called semi-hardness temperature T.sub.H, which is obtained from a softening curve (which in graphical form is the Vickers hardness HV plotted as a function of the annealing temperature T). The semi-hardness temperature T.sub.H is thereby associated with the value: ##EQU1## A thermal stress occurs during fastening of the semiconductor component on the base, when the adhesive is hardened or a eutectic reaction is caused between the silicon element and the gold coating of the base. Furthermore, high temperatures occur during the connection of the semiconductor component to the small connecting legs with so-called bonding wires and during pressing of the complete component into plastic. During these manufacturing steps, temperatures of up to 400.degree. C. can occur over a time period of 1 hour. Therefore, no noticeable softening should be recognized in the semiconductor base materials below 350.degree. to 400.degree. C. PA1 (c) The electrical and thermal conductivity should be as high as possible so that power loss created during operation of the silicon semiconductor can be discharged in the form of heat and in this manner a self-destruction of the component is prevented. In order to assure the heat discharge to the necessary degree, the electrical conductivity should, as much as possible, lie above 80% IACS. (100% IACS corresponds with 58.00 m/OHM x mm.sup.2). PA1 (d) The material must be substantially resistant to oxidation of its surface so that, during the manufacturing steps which take place at an elevated temperature, the smallest possible oxide cover on the base surface is created, thereby assuring that the adhesion between the silicon component, the bond wires and the plastic mass does not deteriorate. For the mentioned use, copper-iron alloys, for example CDA 194, have previously been used to a great degree. These materials have sufficient hardness and good bending behavior and a substantial oxidation stability, but the electrical conductivity is approximately 60 to 70% IACS so that, in the case of high-performance semiconductors, sufficient heat dissipation does not exist. Other low-alloyed materials, as for example CuZnO 0.15, CuSnO 0.12, or CuFeO 0.1, do achieve an electrical conductivity above 80% IACS, but due to the high copper content, have at higher temperatures a tendency toward greater surface oxidation. A low-alloyed CuNiSn-alloy with 0.03 to 0.5% Ni and 0.03 to 0.5% Sn according to Japanese Published Application No. 48-19425 does have sufficient electrical conductivity, but only a relatively low semi-hardness temperature. PA1 0.03 to 0.2% nickel by weight; PA1 0.03 to 0.2% tin by weight; and PA1 0.015 to 0.1% titanium by weight; the remainder being copper and common impurities. PA1 0.03 to 0.06% nickel by weight, PA1 0.03 to 0.06% tin by weight; and PA1 0.015 to 0.03% titanium by weight. PA1 (a) homogenized at temperatures of 850 to 950.degree. C. between 1 and 24 hours. PA1 (b) hot rolled at temperatures of 600 to 800.degree. C. in one or more passes, and PA1 (c) cooled off to room temperature with a cooling-off speed of between 10.degree. C./min. and 2000.degree. C./min.
Furthermore, it is known that, upon occurrence of the usual contamination, strong variations in characteristics can occur in low-alloyed materials.